This sort of moving object detection apparatus is used as, for example, a crime prevention device or the like. For example, Japanese Patent Application Publication No. H09-272402 issued Oct. 21, 1997 discloses ultrasonic Doppler type intrusion detection apparatus for vehicle (hereinafter also referred to as “first conventional apparatus”). This apparatus comprises first and second judgment means, and is configured to operate intermittently. The first judgment means judges whether or not a Doppler shift value is in a set range representative of unlawful entry of a person into a vehicle. At this point, the apparatus counts the number of times the first judgment means judges that a Doppler shift value is in the set range, and then obtains a count value. The second judgment means judges whether or not the count value reaches a predetermined value. When the count value reaches the predetermined value, the apparatus gives an alarm. In this apparatus, unlawful entry can be detected without the influence of disturbance. Moreover, since the apparatus operates intermittently, power consumption can be reduced.
Japanese Patent Publication No. S62-43507 issued Sep. 14, 1987 discloses moving object detection apparatus (hereinafter also referred to as “second conventional apparatus”). This apparatus is configured to extract cosine and sine component signals from an output signal for generating ultrasonic waves and an input signal obtained from incoming ultrasonic waves and to convert the cosine and sine component signals into binary signals to set to X and Y coordinates of X-Y coordinate system, respectively. Since an X coordinate value is 1 or 0 and a Y coordinate value is also 1 or 0, a coordinate point (X, Y) corresponds to any quadrant of the coordinate system. And the apparatus judges that a moving object approaching the apparatus exists in a detection area if (X, Y) turns counterclockwise around the origin of the coordinate system, and judges that a moving object leaving the apparatus exists in the detection area if (X, Y) turns clockwise. In this prior art, existence of a moving object approaching or leaving the apparatus can be certainly detected without frequency analysis.
Japanese Patent Application Publication No. H01-189582 issued Jul. 28, 1989 discloses moving object detection apparatus (hereinafter also referred to as “third conventional apparatus”). This apparatus judges whether or not a moving object approaching or leaving an ultrasonic receiver exists in a detection area based on two Doppler signals in the same way as the second conventional apparatus. The apparatus then increases a count value for an alarm in response to the existence of the moving object approaching the receiver and decreases the count value in response to the existence of the moving object leaving the receiver. In this apparatus, the influence caused by the swing of a curtain(s) can be avoided.
In case of the first conventional apparatus, since the apparatus operates intermittently, power consumption can be reduced. However, since the apparatus includes a microcomputer and needs to take a Doppler shift value through an A/D converter, there is an issue that power consumption is increased with the A/D conversion.
In case of the second conventional apparatus and the third conventional apparatus, since each apparatus includes a pair of binary converters, a pair of level detection circuits and an OR circuit, simplified construction is desired in addition to reduction of power consumption.